The present invention relates generally to equipment utilized in subterranean wells and, in an embodiment described herein, more particularly provides a torque resistant retrievable whipstock.
When a milling tool or other cutting tool is deflected off of a whip stock or other deflection device, a torque may be imparted to the whipstock due to rotation of the cutting tool. This torque may cause the whipstock to become misaligned relative to the well in which it is installed. Where the objective is to cut a window through casing lining the well, it is generally desired for the window to face a particular direction, and misalignment of the whipstock would prevent accurate placement of the window. Therefore, it would be advantageous to provide a whipstock or other deflection device which is capable of resisting torque applied to it.
In a window milling operation, it may be desired to isolate the wellbore below the whipstock from the portion of the wellbore in which the window milling operation is being performed. For this purpose, the whipstock may be sealingly attached to a packer set in the wellbore below the whipstock. In these cases, the packer also serves as an anchoring device for securing the whipstock within the wellbore.
When the whipstock is no longer needed, it may be retrieved from the well, or it may be milled or drilled through to provide access to and fluid communication with the wellbore therebelow. Milling and drilling of the whipstock are sometimes time-consuming operations and do not facilitate later connection of equipment thereto, thus, it would be advantageous to be able to conveniently retrieve the whipstock, while leaving a large diameter seal bore attached to the packer. In this manner equipment could be subsequently sealingly engaged with the seal bore, and equipment could be passed conveniently through the large diameter to the wellbore below the packer.
Unfortunately, where the whipstock has been sealingly attached to the packer during milling or drilling operations, it may prove difficult to disengage the whipstock from the packer. Fluid pressure differences between the wellbore above and below the packer acting on the large diameter seal bore can cause large forces to be imparted to the assembly. Therefore, it would be advantageous to reduce the effects of forces acting on the assembly due to fluid pressure, while still permitting the whipstock to be conveniently separated from the packer and leaving a large diameter seal bore after such separation.